Applicability of Statistical Descriptions of AerMet100 Steel Subjected to Different Triaxial Stress States for Fracture Calculations

Computational continuum codes can provide many details on the response of metals to explosive loading. However, most “production” level calculations use a homogeneous description of the metal. This is an incorrect representation since metals possess a microstructure whose details create variations in material strength and other properties such as strain to failure. Ultimately these variations influence the formation of fragments at the macroscopic level. The spatial scale of the microstructure is on the order of micrometers and is not readily accessible to current computational tools and resources for system level calculations. Rather than explicitly model the microstructure one can attempt to capture the effects of material non-homogeneity through the use of a statistical description. Specifically, a statistically compensated Johnson-Cook fracture model can be used to simulate the non-homogeneity of a material. This analysis proceeded in two steps using experimental data available from earlier fragmentation work conducted on AerMet100 steel. In those experiments, a sphere was fractured by impact with a thin plate and a cylinder was fractured through explosive loading. Therefore, the sphere and the cylinder experienced significantly different triaxial stress states. In the first step, the distribution of failure strains required to produce an accurate solution for the explosively loaded cylinder was determined via Eulerian-Lagrangian calculations using Sierra Fortissimo. Sierra Fortissimo is a tool that allows for different code coupling techniques between CTH and Sierra Presto. In the second step, this distribution was applied to the sphere impact using the explicit dynamics code Sierra Presto. Comparisons of the sphere calculation results are made to the experimental fragmentation data and the results are analyzed in the context of triaxial stress states.